1. Field of the Invention
The invention relates to flight control systems, particularly with regard to the takeoff mode thereof.
2. Description of the Prior Art
In modern aircraft requiring a takeoff run to become airborne, the pilot applies a pitch-up command to the control column when the aircraft attains a predetermined forward velocity, designated as the rotation velocity V.sub.R. The manual command from the pilot rotates the craft about the main gear so as to increase the angle of attack thus lifting the craft from the runway. To achieve specified takeoff performance, the manual command must be precisely applied to rotate the craft at a predetermined pitch rate to asymptotically capture a predetermined climb-out pitch attitude.
In most aircraft, this maneuver requires complete pilot attention and a nominal degree of pilot skill. In other aircraft, particularly the short takeoff and landing variety, hereinafter referred to as STOL aircraft, the maneuver is critical with regard to aircraft safety. In STOL aircraft, because of the narrow stall margin configurations thereof, the pilot must precisely command a high maximum pitch rate and capture the predetermined climb-out pitch attitude with no overshoot thereof. In the STOL aircraft, over-rotation causes excessive angle of attack and the attendant lack of forward acceleration; conversely, under-rotation causes the aircraft to become airborne beyond the designated takeoff point. Thus, in the short runway STOL environment, it is clear that the takeoff maneuver must be precise or the aircraft will over-run the runway surface without having become airborne. This maneuver is difficult to manually execute through elevator control because of the lack of adequate guidance information and the high forces and large elevator deflections required. Even with an elevator boost system which reduces the required force inputs, the rotation maneuver is difficult to perform precisely. With such aircraft, pilots tend to vary the pitch rate in an attempt to hunt for and seek the required pitch attitude. Such maneuvering is considered to be dangerous because of the aforementioned narrow stall margin configuration of such STOL aircraft.